The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
3GPP third generation partnership project
ACK acknowledgement
eNB evolved NodeB (BS of a LTE/LTE-A system)
FDD frequency division duplexing
HARQ hybrid automatic repeat request
LTE long term evolution (evolved UTRAN)
LTE-A long term evolution advanced
NACK negative acknowledgement
PSS primary synchronization signal
RAT radio access technology
RF radiofrequency
SSS secondary synchronization signal
TDD time division duplexing
TX transmission
UE user equipment
UTRAN universal terrestrial radio access network
WLAN wireless local area network (sometime termed WiFi)
Wireless radio operations in licensed frequency bands has been utilized to such an increasing extent that portions of the radio spectrum that still remain available have become limited. Various network operators, service providers, communication device manufacturers, and communication system manufacturers are therefore seeking efficient solutions to utilize unlicensed frequency bands, also termed shared band or bands and more formally as license-exempt bands. Communication on an unlicensed shared band is generally based on sharing an available channel between different communication devices. The different communication devices may utilize a common RAT, but in certain scenarios the different communication devices may utilize different RATs.
In an unlicensed shared band the channel access can be distributed, in which the communication devices detect a channel and utilize a channel reservation scheme known to other communication devices in order to reserve a right to access the channel. In distributed channel access, a transmitting communication device and a receiving communication device are generally not synchronized to a global reference. Transmissions on an unlicensed shared band that do not utilize a common timing reference (one shared by both the transmitting communication device and the receiving communication device) are generally short in duration in order to allow multiple communication devices to share the channel. Generally, in this scenario a transmitting communication device only transmits a few packets at a time before the transmitting communication device defers its access to some other transmitting communication device that also occupies the channel. After a random duration, the first transmitting communication device then transmits again. Therefore specific measures are required in order to initially synchronize the transmitting communication device and receiving communication device at the beginning of each data transmission. This is sometimes done by synchronizing the receiving communication device with the data transmission (that is, informing the receiving communication device when the first packet of the data transmission begins).
In addition to synchronization, the transmitting communication device can indicate frequency resources that can be utilized for transmission. In general a transmitting communication device may only utilize a portion of the frequency resources, and can indicate to the receiving communication device which portion of the frequency resources the transmitting communication device will utilize for transmission. In one prior art technique for communicating in the license-exempt band, a transmitter sends at least two synchronization sequences having cyclic shift characteristics prior to the data transmission. The intent is that the first sequence is used to synchronize the receiver and the cyclic shift in the subsequent sequence(s) is/are used to inform the receiver about the radio resources being used for the data transmission. The resource mapping between the cyclic shift that the receiver observes and actual radio resources used by the transmitter can be implemented using a tree-based method such as that shown at FIG. 1. The unlicensed bandwidth is divided into predetermined channels and the transmitted cyclic shift maps to a specific radio resource or resources on a specific channel. Those teachings are not seen to provide an efficient manner for organizing feedback from the receiver to the transmitter, such as ACK and NACK messages.
The WLAN family of standards (IEEE 802.x) transmit MAC level feedback on the same resource as the actual data transmission after a short interframe space SIFS period (10 us). This is not seen to be efficient for broader implementation since the feedback thereby requires the whole bandwidth used by the WLAN for transmitting the original data. The LTE system conveys its uplink hybrid automatic repeat request HARQ ACK/NACK feedback for a dynamically scheduled downlink data transmission on a physical uplink control channel PUCCH channel which is derived from the physical downlink shared channel PDSCH on which the data was sent. Or alternatively if there is an uplink resource allocated for the time the feedback is to be sent the LTE system multiplexes the feedback with that uplink data sent on the allocated physical uplink shared channel PUSCH.
While there are many proposals for exactly how communications in the unlicensed band should be managed among the various devices seeking access, operation in the unlicensed shared band generally involves sharing one or more channels in a communication system between one or more communication devices, where the communication devices can utilize different RATs. What is needed is a way to provide effective asynchronous/contention-based access over a shared band with dynamic and scalable spectrum allocation. This is not only for expanding the available spectrum over which user devices may communicate but also to support ad hoc networked wireless mobile robotics which currently operate primarily using IEEE standards such as 802.11 and 802.15.4. These teachings provide a feedback mechanism which may be advantageously used in the unlicensed band, and which is scalable and dynamic with minimal added control signaling.